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Abstract:

A method for filling cooling holes in a component of a gas turbine engine
is disclosed. The component may include a plurality of first cooling
holes penetrating the wall of the component. The method may comprise the
steps of exposing the outer surface of the component, filling the
plurality of first cooling holes of the component with a filling agent,
curing the filling agent to block the passage of air through the cooling
holes, and applying a thermal barrier coating over the surface of the
component. The method may further include installing a second plurality
of cooling holes, the second plurality of cooling holes penetrating the
thermal barrier coating and the wall of the component and allow air to
pass therethrough.

Claims:

1. A method for filling cooling holes in a component of a gas turbine
engine, the component having an outer surface and an inner surface and a
plurality of first cooling holes, the plurality of first cooling holes
extending between the outer surface and the inner surface of the
component, the method comprising the steps of: exposing the outer surface
of the component; filling the plurality of first cooling holes with a
filling agent; and curing the filling agent to block the plurality of
first cooling holes.

2. The method of claim 1 wherein the step of exposing the outer surface
of the component comprises the step of removing a first thermal barrier
coating from the outer surface of the component.

3. The method of claim 2 wherein the first thermal barrier coating
comprises a first ceramic top coating overlying a first metallic bond
coating.

4. The method of claim 1 further comprising the step of applying a second
thermal barrier coating over the outer surface of the component after the
step of curing the filling agent.

5. The method of claim 4 wherein the second thermal barrier coating
comprises a second ceramic top coating overlying a second metallic bond
coating.

6. The method of claim 4 further comprising the step of installing a
plurality of second cooling holes, the plurality of second cooling holes
penetrating the second thermal barrier coating and extending between the
outer surface and the inner surface of the component.

7. The method of claim 6 wherein the step of curing the filling agent to
block the plurality of first cooling holes obstructs cooling fluid flow
through the plurality of first cooling holes.

8. The method of claim 6 further comprising the step of removing excess
filling agent from the outer surface of the component prior to the step
of curing the filling agent to level the outer surface for application of
the second thermal barrier coating.

9. The method of claim 6 further comprising the step of removing excess
filling agent from the outer surface of the component after the step of
curing the filling agent to level the outer surface for application of
the second thermal barrier coating.

10. The method of claim 6 wherein the filling agent is selected from the
group consisting of an enamel and a ceramic paste.

11. The method of claim 10 wherein the enamel is vitreous enamel.

12. The method of claim 10 wherein the enamel is stoved enamel.

13. The method of claim 10 wherein the ceramic paste is waterglass.

14. The method of claim 10 wherein the ceramic paste is a waterglass
slurry.

15. The method of claim 10 wherein the filling agent comprises a metal
alloy powder to provide surface uniformity between the plurality of
filled first cooling holes and the component.

16. The method of claim 10 wherein the step of filling the plurality of
first cooling holes with the filling agent is performed by dipping the
component in the filling agent.

17. A method for filling cooling holes in a component of a gas turbine
engine, the component having an outer surface and an inner surface and a
plurality of first cooling holes, the first cooling holes extending
between the outer surface and the inner surface of the component, the
method comprising the steps of: exposing the outer surface of the
component; filling the plurality of first cooling holes with a filling
agent; curing the filling agent to block the plurality of first cooling
holes; and applying a thermal bather coating over the outer surface of
the component.

18. The method of claim 17 further comprising the step of installing a
plurality of second cooling holes, the plurality of second cooling holes
penetrating the thermal barrier coating and extending between the outer
surface and the inner surface of the component.

19. The method of claim 17 wherein the filling agent is selected from the
group consisting of an enamel and a ceramic paste.

20. A component of a gas turbine engine comprising: a plurality of first
cooling holes extending between an outer surface and an inner surface of
the component, the plurality of first cooling holes being filled with a
filling agent selected from the group consisting of an enamel and a
ceramic paste, the filling agent being cured to solid form to block the
flow of cooling fluid though the plurality of first cooling holes; a
thermal barrier coating over the outer surface of the component; and a
plurality of second cooling holes penetrating the thermal barrier coating
and extending between the outer surface and the inner surface, the
plurality of second cooling holes allowing cooling fluid to pass
therethrough.

Description:

FIELD OF THE DISCLOSURE

[0001] The present disclosure generally relates to a gas turbine engine
and, more particularly, relates to the closure of cooling holes of a
component within a gas turbine engine.

BACKGROUND OF THE DISCLOSURE

[0002] A gas turbine engine commonly includes a fan section, a compressor,
at least one combustor, and a turbine. The compressor and turbine each
include a number of rows of blades attached to a rotating cylinder. In
operation, the air is pressurized in a compressor and is then directed
toward the combustor. Fuel is continuously injected into the combustor
together with the compressed air. The mixture of fuel and air is ignited
to create combustion gases that enter the turbine, which is rotatably
driven as the high temperature and high pressure combustion gases expand
in passing over the blades forming the turbine. Since the turbine is
connected to the compressor via a shaft, the combustion gases that drive
the turbine also drive the compressor, thereby restarting the ignition
and combustion cycle.

[0003] Since the gas turbine engine operates at high temperatures, certain
components of the gas turbine engine, such as linear flowpath liners, the
turbine, combustor and augmentor, are directly exposed to hot combustion
gases, the temperatures of which sometimes exceed the melting temperature
of the materials used in the engine components in contact with these hot
gases. To prevent damage to the components, solutions are needed to
shield the components from excessive heat.

[0004] One common solution is to protect the exposed surfaces of the
components with a coating system, for example, a thermal barrier coating
(TBC) which typically includes a metallic bond coat and a layer of
ceramic deposited on the metallic bond coat layer. A typical metallic
bond coat includes, for example, MCrAlY, wherein M is Ni, Co, Fe or
mixtures thereof. The metallic bond coat provides oxidation and corrosion
resistance and accommodates residual stresses which might develop in the
coating system. A commonly applied ceramic material is yttria stabilized
zirconia (YSZ), which exhibits resistance to thermal shock and thermal
fatigue even at 1150° C. (2102° F.). Methods, such as air
plasma spraying (APS), low pressure plasma spraying (LPPS), or a physical
vapor deposition (PVD) process, such as electron beam physical vapor
deposition (EBPVD) are typically used to deposit the ceramic layer on the
metallic bond coat.

[0005] In addition to applying a TBC to the surface of the affected
components, internal cooling of selected engine components, such as
turbine blades, nozzles, and liners is employed to further protect the
underlying component substrates. To accomplish effective cooling, a
complex cooling scheme is usually installed by forcing bleed air to exit
from cooling holes on the flowpath surface and form a suitable film of
cooling air over the flowpath surface.

[0006] When a TBC is damaged during operation or when a new design of TBC
needs to be installed, the old TBC often needs to be removed before the
new TBC is applied. However, the presence of open cooling holes on the
exposed surface of the engine component poses a significant problem for
the successful application of a new, high quality TBC layer.
Specifically, a non-uniform (or uncompacted) TBC surface susceptible to
spallation frequently results when a new TBC layer is directly applied
over pre-existing open cooling holes remaining after removal of the old
TBC layer. In particular, since new cooling holes are drilled to meter a
specific quantity of cooling air on the engine component after a new TBC
layer is applied, any subsequent coating spallation may lead to opening
of the pre-existing holes and cause an increase in cooling air flow on
the component, as cooling air flow is metered by the size and quantity of
the cooling holes. The increase in cooling air flow on the component may
subsequently starve other downstream components of cooling air causing
the downstream components to suffer from structural damage associated
with operating at higher than designed temperatures.

[0007] It is known that typical weld or braze repair processes may be used
to obstruct (block) old cooling air holes. One problem with the brazing
approach is that a typical braze material will incrementally lower the
incipient melting temperature of areas of inhomogeneous chemistry in the
metal alloy of the component, especially on castings, due to the
diffusion of boron or silicon into the base metal alloy from the braze
material. A second problem with brazing is that wrought alloy properties
will be reduced by exposure to brazing process temperatures. Lower
melting brazes could be prone to re-melting and with a possibility of
resolidifying elsewhere on alloys adversely affected by exposure to the
low melting braze constituents. Welding attempts of the old set of
cooling holes has proven to introduce substantial distortion into the
part associated with solidification of the welds. For both weld and braze
repairs, precipitation hardenable alloys such as Inconel 718 or Waspoloy
will usually be distorted by the post weld/braze heat treatment required
to restore the alloy to a serviceable condition.

[0008] To better address the challenges raised by the gas turbine industry
to produce reliable and high-performance gas turbines engines, and in
particular, to provide engine components with better designed cooling
holes, it is desirable to provide a method for filling cooling holes.
Specifically, a method which effectively blocks cooling holes of the
component of interest to produce a durable component surface before
application of a new TBC is desired. It is also desirable that the
materials used to block the cooling holes do not induce any structurally
detrimental effects in the component material.

SUMMARY OF THE DISCLOSURE

[0009] In accordance with one aspect of the present disclosure, a method
for filling cooling holes in a component of a gas turbine engine is
disclosed. The component may have an outer surface and an inner surface.
The component may have a plurality of first cooling holes which extend
between the outer and inner surfaces of the component. The method may
comprise the steps of: exposing the outer surface of the component,
filling the plurality of first cooling holes with a filling agent, and
curing the filling agent to block the plurality of first cooling holes.

[0010] In another refinement, the step of exposing the outer surface of
the component may comprise the step of removing the first thermal barrier
coating from the outer surface of the component.

[0011] In another refinement, the first thermal barrier coating may
comprise a first ceramic top coating overlying a first metallic bond
coating.

[0012] In another refinement, the method may further comprise the step of
applying a second thermal barrier coating over the outer surface of the
component after the step of curing the filling agent.

[0013] In another refinement, the second thermal barrier coating may
comprise a second ceramic top coating overlying a second metallic bond
coating.

[0014] In another refinement, the method may further comprise the step of
installing a plurality of second cooling holes and the plurality of
second cooling holes may penetrate the second thermal barrier coating and
extend between the outer and inner surfaces of the component.

[0015] In another refinement, the step of curing the filling agent to
block the plurality of first cooling holes may prevent cooling fluid to
pass through the plurality of first cooling holes.

[0016] In another refinement, the method may further comprise the step of
removing excess filling agent from the outer surface of the component
prior to the step of curing the filling agent to level the outer surface
for application of the second thermal barrier coating.

[0017] In another refinement, the method may further comprise the step of
removing excess filling agent from the outer surface of the component
after the step of curing the filling agent to level the outer surface for
application of the second thermal barrier coating.

[0018] In another refinement, the filling agent may be an enamel.

[0019] In another refinement, the enamel may be in paint form.

[0020] In another refinement, the enamel may be vitreous enamel.

[0021] In another refinement, the enamel may be stoved enamel.

[0022] In another refinement, the filling agent may be a ceramic paste.

[0023] In another refinement, the ceramic paste may be waterglass.

[0024] In another refinement, the filling agent may comprise a metal alloy
powder to provide surface uniformity between the first cooling holes and
the surrounding surface of the component.

[0025] In another refinement, the step of filling the plurality of first
cooling holes with the filling agent may be performed by dipping the
component in the filling agent.

[0026] In another refinement, the step of filling the plurality of first
cooling holes with the filling agent may be performed by applying the
filling agent to the cooling holes with a spraying device, a brush, or a
roller.

[0027] In another refinement, the step of filling the plurality of first
cooling holes with the filling agent may be performed by screeding.

[0028] In another refinement, the filling agent may be capable of
withstanding a temperature of more than 550° C. without
deterioration of the gas turbine engine.

[0029] In accordance with another aspect of the present disclosure, a
method for filling cooling holes in a component of a gas turbine engine
is disclosed. The component may have an outer surface and an inner
surface. The component may have a plurality of first cooling holes which
extend between the outer and inner surfaces of the component. The method
may comprise the steps of: exposing the outer surface of the component,
filling the plurality of first cooling holes with a filling agent, curing
the filling agent to block the plurality of first cooling holes, and
applying a thermal barrier coating over the outer surface of the
component.

[0030] In accordance with another aspect of the present disclosure, a
component of a gas turbine engine is disclosed. The component may have a
plurality of first cooling holes extending between an outer surface and
an inner surface of the component. The plurality of first cooling holes
may be filled with filling agent and the filling agent may be cured to
solid form to block the flow of cooling fluid through the plurality of
first cooling holes. The outer surface of the component may be coated
with a thermal bather coating. The component may further comprise a
plurality of second cooling holes penetrating the thermal barrier coating
and extending between the outer surface and the inner surface. The
plurality of second cooling holes may allow cooling fluid to pass
therethrough.

[0031] Further forms, embodiments, features, advantages, benefits, and
aspects of the present disclosure will become more readily apparent from
the following drawings and descriptions provided herein.

[0033] FIG. 2 illustrates a top perspective view of a substrate wall that
may be modified according to the present disclosure;

[0034] FIG. 3 is a side cross-sectional view through the section 2-2 of
FIG.2, illustrating the substrate wall, in accordance with the present
disclosure;

[0035] FIG. 4 is a side cross-sectional view of the substrate wall shown
in FIG. 3, showing the filling of cooling holes with a filling agent
after removing the original TBC layer, according to the present
disclosure;

[0036] FIG. 5 is a side cross-sectional view of the substrate wall shown
in FIG. 4 after removing excess filling agent from the inner and outer
surfaces of the substrate wall;

[0037] FIG. 6 is a side cross-sectional view of the substrate wall shown
in FIG. 5 after the application of a new TBC layer according to the
present disclosure; and

[0038] FIG. 7 is a side cross-sectional view of the substrate wall shown
in FIG. 6 after the installing new cooling holes according to the present
disclosure.

[0039] Before proceeding with the detailed description, it is to be
appreciated that the following detailed description is merely exemplary
in nature and is not intended to limit the invention or the application
and uses thereof. In this regard, it is to be additionally appreciated
that the described embodiment is not limited to use in conjunction with a
particular type of ceramic spray shield or gas turbine. Hence, although
the present disclosure is, for convenience of explanation, depicted and
described as shown in certain illustrative embodiments, it will be
appreciated that it can be implemented in various other types of
embodiments and equivalents, and in various other systems and
environments.

DETAILED DESCRIPTION OF THE DISCLOSURE

[0040] Referring now to the drawings, and with specific reference to FIG.
1, there is depicted an exemplary gas turbine 10 wherein various
embodiments of the present disclosure may be utilized. In this example,
the industrial gas turbine 10 may include a compressor section 11 which
may comprise, sequentially from the forefront of the gas turbine engine
10, a fan 12, a low pressure compressor 14, a high pressure compressor
16, a combustor chamber 18 downstream of the compressor section 11, a
high pressure turbine 20 and a low pressure turbine 22 both downstream of
the combustor chamber 18, a tail cone 24, and an exhaust nozzle 26.
Further, a high pressure shaft 28 may couple the high pressure compressor
16 with the high pressure turbine 20, while a low pressure shaft 30 may
couple the low pressure compressor 14 with the low pressure turbine 22.
Both shafts 28 and 30 may be rotatable about an axis A. The low pressure
shaft 30 may drive the fan 12 through a gear train 32. On the outside, a
fan nacelle 34 may surround both the fan 12 and a core nacelle 36, and
may support the core nacelle 36 through pylon structures 38 commonly
referred to as upper and lower bifurcations. The core nacelle may house
the compressors 14 and 16, the combustor chamber 18, the turbines 20 and
22, and the tail cone 24.

[0041] In the example shown in FIG. 1, the engine 10 may be a high bypass
turbofan arrangement. During operation, part of the air suctioned by the
fan 12 may bypass the core nacelle 36 and enter a generally annular
bypass flow path 40 which is arranged between the confines of the fan
nacelle 34 and core nacelle 36. The rest of the air may be directed into
the core nacelle 36, pressurized in the compressors 14 and 16, and mixed
with fuels in the combustor 18 to generate hot gases. The hot gases may
expand in and flow through the turbines 20 and 22, which extract energy
from the hot gases. The turbines 20 and 22 may then power the compressors
14 and 16 as well as the fan 12 through rotor shafts 28 and 30. Finally,
the exhaust gases may exit the gas turbine engine through the exhaust
nozzle 26. In power generation applications, the turbines 20 and 22 may
connect to an electric generator to generate electricity. In aerospace
applications, the exhaust of the turbine 10 can be used to create thrust.

[0042] The annular outer and inner liners (not shown) of the combustion
chamber 18 bound the combustion process during operation. A portion of
the pressurized cooling air is diverted from compressor 16 or other
cooling air source and is channeled around the annular outer and inner
liners to facilitate cooling during operation. Cooling air is metered
through small apertures in the liners to establish a film of cooler air
to further reduce the temperature of the liner walls.

[0043] Turning now to FIG. 2, a top perspective view of a substrate wall
60 is illustrated. The substrate wall 60 may be modified by the present
method and may be used with or form a part of components within a gas
turbine engine 10 (shown in FIG. 1). Such components may be, but are not
limited to, the various engine components described above. For example,
the substrate wall 60 may be used with or form a part of components such
as, but not limited to, liner flowpath panels, combustor liners, ducts,
and nozzles. In addition, the substrate wall 60 may be made from a
superalloy metal having the ability to withstand high temperatures during
operation of the engine. For example, the substrate wall 60 may be made
from, but is not limited to, materials such as nickel or cobalt based
superalloys. For liners and ducts further downstream, air stream
temperature drops, so alloys with lower temperature capabilities such as,
but not limited to, corrosion resistant steel or titanium may also be
used.

[0044] FIG. 3 is a side cross-sectional view through the section 3-3 of
FIG. 2, illustrating substrate wall 60. As shown in FIGS. 2-3, the
substrate wall 60 may include an outer surface 62 and an opposite inner
surface 64. The wall 60 may be perforated or porous and may include a
plurality of cooling holes 66, 68, and 70 which are distributed in a
spaced relationship across wall 60, as shown. The cooling holes 66, 68,
and 70 may extend between the outer and inner surfaces 62 and 64,
respectively, as shown. Further, although the shapes of the cooling holes
can be a circle or an oval as shown in FIG. 2, other shapes and relative
orientations of the cooling holes are possible.

[0045] As shown in FIG. 3, each cooling hole 66, 68, and 70 may include an
exhaust side 72 and an opposite inlet side 74, as shown. Although the
cooling holes 66, 68, and 70 are shown extending substantially
perpendicularly through the substrate wall 60 with respect to surfaces 62
and 64, cooling holes 66, 68, and 70 may be obliquely oriented with
respect to the surfaces 62 or 64 or may adopt other orientations as well.

[0046] As illustrated in FIGS. 2 and 3, the cooling holes 66, 68, and 70
may be substantially cylindrical and may have a diameter, for example,
between about 0.02 mm and about 0.1 mm, between about 0.1 mm and about
0.4 mm, between about 0.4 and about 0.7 mm, between about 0.7 mm and
about 1.0 mm, and between 1.0 mm and about 1.5 mm. In addition, the
cooling holes 66, 68, and 70 may have the same or different diameters
with respect to each other.

[0047] During operation, combustion gas 80 may flow past the outer surface
62, and cooling fluid 82 may be channeled across the inner surface 64, as
shown. Cooling fluid 82 may comprise cooling air or another suitable
cooling fluid in gas or liquid form. To insulate the substrate wall 60
from the hot combustion gas 80, the wall outer surface 62 may be covered
by a thermal bather coating (TBC) 84, in whole or in part, as desired.
TBC 84 may facilitate protecting the outer surface 62 from the combustion
gas 80. TBC 84 may comprise a top coating 83 and a metallic bond coating
86, as shown. The top coating 83 may comprise ceramic such as thermally
resistant yttria stabilized zirconia (YSZ) or another suitable
composition. The metallic bond coating 86 may comprise a material that
provides oxidation and corrosion resistance and accommodates residual
stress. Metallic bond coating 86 may be a metallic material such as, but
not limited to, MCrAlY, wherein M is Ni, Co, Fe, or mixtures thereof. The
metallic bond coating 86 may be laminated between the wall outer surface
62 and top coating 83 in order to help enhance the bonding of TBC 84 to
the substrate wall 60.

[0048] As shown in FIG. 3, TBC 84 may cover the wall outer surface 62 and
may not extend over the cooling hole inlet sides 74, as shown. As such,
the cooling fluid 82 may be channeled through cooling holes 66, 68, and
70 and through the TBC layer 84 to facilitate cooling an outer surface 88
of TBC 84. However, TBC 84 may extend over a portion of the cooling hole
inlet sides 74 but not block the cooling holes completely.

[0049] During engine operation, the original TBC 84 may need to be
replaced for various reasons. Sometimes a new pattern of cooling holes
may be more desirable or advantageous. Sometimes the original TBC 84 may
be damaged and may have to be replaced and/or repaired. Sometimes an
improved TBC coat may be needed to replace an older system. Sometimes a
TBC coat may need to be applied to outer surface 62 in order to upgrade
the component. However, if a new TBC layer is directly applied over open
cooling holes 66, 68, and 70 on an exposed outer surface 62 of substrate
60, then a non-uniform (or uncompacted) metallic bond coat may be formed
under the ceramic top coat in the newly applied TBC layer. This may
result in a new TBC layer that is susceptible to fragmentation and/or
spallation. After new cooling holes are installed in the substrate wall
60, such unwanted spallation on the TBC layer could lead to opening of
the original cooling holes 66, 68, and 70 and produce a corresponding
increase in cooling fluid flow on the substrate 60 which may ultimately
cause the starving of other downstream components of cooling fluid. In
order to remedy this potential problem, cooling holes 66, 68, and 70 may
be blocked or obstructed with a filling agent after exposing outer
surface 62 and before application of a new TBC layer.

[0050] FIG. 4 shows a side cross-sectional view of substrate wall 60,
showing the filling of cooling holes 66 and 68 with a filling agent 100
after exposing outer surface 62 by removing the original TBC layer 84.
First, TBC 84 may be removed from the outer surface 62 of the substrate
60 using a method or a process known to a skilled artisan to afford an
exposed outer surface 62 of substrate wall 60, as shown. Alternatively,
removal of another type of coating on outer surface 62 may be required to
expose outer surface 62 if a coating other than a TBC is used.
Alternatively, removal of TBC 84 (or another type of coating) may not be
required to expose outer surface 62 if a TBC layer is to be applied to
outer surface 62 for the first time. After exposure of outer surface 62,
a filling agent 100 may be used to fill the cooling holes 66 and 68, as
shown in FIG. 4.

[0051] Filling agent 100 may be an enamel such as vitreous enamel, stoved
enamel, or an enamel in paint form. Alternatively, filling agent 100 may
be a ceramic paste, such as waterglass or a waterglass slurry. The
filling agent 100 may comprise waterglass or other similar ceramic
materials that chemically react to solidify. The filling agent 100
compositions used to block the cooling holes preferably are stable at
high temperatures. After filling the cooling holes with filling agent
100, the filling agent 100 may then be thermally dried and cured at the
appropriate temperature, for example between about 175° C.
(-350° F.) to about 370° C. (-700° F.) for providing
solidified resin-based enamels, and at higher temperatures for ceramic
pastes. However, the skilled artisan will understand that depending on
the type of filling agent used as well as other conditions such as the
type of substrate wall, other curing temperatures may be appropriate.

[0052] In general, filling agent 100 may comprise fillers such as a glass
frit, metal alloy powder, and a matrix material such as organic resin,
silicone resin, or ceramic binders such as silicates/waterglass or
similar ceramic slurries. The filling agent 100 may be applied to a
desired region of the substrate wall and subsequently heated to cure the
resin or solidify/fuse the inorganic enamel or ceramic paste to the
surface of the substrate. The glass frit or frits that comprise the
precursor may be prepared utilizing conventional glass melting
techniques. A conventional ceramic refractory, fused silica, or platinum
crucible may be used to prepare the glass frit. For instance, selected
oxides may be smelted at, for example, about 1250° C. for about 30
minutes. The molten glass formed in the crucible is then converted to
glass frit using water-cooled rollers and milling equipment. Any of the
various techniques to prepare the fits may be known to and employed by a
skilled artisan.

[0053] On one hand, the glass frit may comprise silica, borax, soda ash,
fluorspar, sodium silica fluoride, clays, electrolytes, and metal oxides.
On the other hand, organic enamel precursors may be provided as well.
These organic enamel precursors may comprise resins, curing agents,
plasticizers, stabilizers, fluidity modifiers, and fillers. In addition,
the resin may allow the enamel or ceramic paste to have the desired
viscosity for application to the substrate walls and allow the enamel or
ceramic paste to bond to the substrate wall. The resin may be any medium
normally used in conventional enamel compositions and may include
solvents, diluents, oils, resin mixtures, petroleum fractions,
film-forming materials, and fillers such as alloy powders and thickeners.
In particular, the addition of metal alloy powders as fillers may act to
improve the similarity between the enamel/ceramic material filling the
cooling holes and the outer and inner surfaces 62 and 64 of substrate 60
that surround the holes.

[0054] The glass frit component may be used in combination with various
mill additions. The mill additions may vary depending upon the specific
application conditions being utilized. For waterglass type ceramic paste
application processes, the glass frits may be milled in conjunction with
other mill additions such as, for example, sodium molybdate, molybdenum
trioxide (molybdic acid hydride/ammonium polymolybdate), sodium silicate,
quartz, and bentonite to produce a suitable composition. As is well-known
in the art, there may be a wide range of other acceptable mill agents or
components that may also be utilized in the present disclosure to produce
the desired product.

[0055] The filling agent 100 may include additional additives such as, for
example, one or more surfactants, to achieve a suitably tacky consistency
that enables the filling agent 100 to adhere to the composition at the
surface of the substrate wall 60. For example, up to about 10 weight
percent of a nonionic surfactant may be used. Examples of surfactants
commercially available for this purpose may include P521A and Merpol from
Witco and Stephan, respectively. Further, filling agent 100 may contain
other filler materials, including but not limited to, glass compositions,
dispersants, metal alloy powders, and/or additional binders/plasticizers
capable of adhering the ceramic powders together. Depending on its
composition, the binder of the filling agent 100 may react at room
temperature, or its reaction may be accelerated by heating such as with a
heat lamp, torch, or other heat source until the strength of the
resulting filler has reached a required level for operation in the gas
turbine engine. Thermal treatments of filling agent 100 may be about
sixteen hours at room temperature to cure a silicone binder, and about
two hours at about 150° C. (302° F.) to react a
phosphate-based binder. However, other thermal treatment conditions are
possible.

[0056] The filling agent 100 according to the present disclosure may be
suitable for application to substrate wall 60 using conventional
techniques such as, for example, either wet or dry application processes.
A suitable wet application process may be dipping. Specifically, in order
to completely fill the cooling holes with filling agent 100 and achieve
complete obstruction of the cooling holes, the substrate 60 may be dipped
in the enamel or ceramic paste composition. Alternatively, the cooling
holes may be filled with filling agent 100 by applying the filling agent
100 (either enamel or ceramic paste) to the cooling holes with a spraying
device, a brush, or a roller. Alternatively, cooling holes may be filled
with filling agent 100 by screeding in which the filling agent 100
(either enamel or ceramic paste) is smeared into the cooling holes using
a spatula or similar tool. However, other application processes for
filling the cooling holes known to a skilled artisan may be used as well.

[0057] Substrate walls that have been treated with the filling agent 100
of the present invention may be heated in a conventional manner using
conventional heating equipment. Heating is generally conducted in an air
convection oven or furnace at a temperature and duration determined
sufficient by a skilled artisan. However, other heating conditions may be
possible.

[0058] The resulting cured filling agent 100 may provide long-term
resistance to the atmospheres and temperatures of, for example, the
compressors of gas turbine engines, and it may be possible to choose such
enamel or ceramic paste in relation to the specified operating
temperature of the engine. For example, it is known that certain enamels
are capable of withstanding temperatures in the order of, for example,
500° C. (932° F.) or higher. However, the filling agent 100
constituents may be able to withstand even higher temperatures and thus
maintain obstruction of the cooling holes even in an event where the
matrix material has been thermally degraded.

[0059] As shown in FIG. 4, filling agent 100 may completely block the
cooling holes at both ends and may obstruct the passage of cooling fluid
through the cooling holes. Alternatively, filling agent 100 may block one
end while substantially blocking the other, or substantially block both
ends. A skilled artisan can make the necessary decision whether an
acceptable degree of blocking is obtained for the cooling holes to
facilitate the subsequent application of a new TBC layer. After the
blocking of cooling holes 66 and 68 with filling agent 100, excessive
enamel or ceramic paste 100 on the inner and outer surfaces of the
substrate wall 60 may be removed by wiping before it cures to reveal the
new, leveled outer and inner surfaces 102 and 104, respectively, as shown
in FIG. 5. Alternatively, excess filling agent 100 may be removed by
abrasive wiping (i.e., sanding) after the curing step. Alternatively,
excess filling agent 100 may be removed from only the outer surface (the
surface to be coated) by wiping or abrasive wiping before or after the
curing step to reveal leveled outer surface 102. Nevertheless, after at
least the outer surface is leveled and the filling agent 100 has fully
cured and dried, a new TBC layer 106 may be applied to leveled outer
surface 102 as described below. Outer surface 102 may be further textured
to facilitate the attachment of a new TBC 106 Importantly, obstruction of
the cooling holes with the cured filling agent 100 and leveling of the
outer surface 102 preferably allows the new metallic bond coat 96 (see
FIG. 6) to be applied against a level surface thus achieving an intended
degree of structural compactness throughout bond coat 96 that is
necessary for avoiding unwanted spallation events.

[0060] Turning now to FIG. 6, a side cross-sectional view of the substrate
wall 60 with a newly deposited TBC 106 is shown. The new TBC layer 106 is
formed by first applying a new metallic bond coat 96 over outer surface
102 and subsequently applying a new ceramic top coat 93 over a new
metallic bond coat 96, as shown. The new TBC layer 106 may completely
cover the cured filling agent 100 on outer surface 102, as shown. The
deposition method for application of the new TBC layer 106 may be a
thermal spray technique or a physical vapor deposition technique or other
suitable processes. The crude surface of the TBC 106 may be polished or
otherwise abraded to give an outer surface 108, as shown.

[0061] Top coat 93 may be a ceramic material which may adhere to metallic
bond coat 96. The ceramic material may comprise a thermally resistant
material such as, but not limited to, yttria stabilized zirconium (YSZ).
Metallic bond coat 96 may be formed from, but is not limited to, MCrALY,
where M is Ni, Co, Fe, or mixtures thereof.

[0062] After TBC 106 is formed, new cooling holes 110 may be installed in
the substrate wall 60 as shown in FIG. 7. The cooling holes 110 may be
installed by a laser or another suitable installation method. Further,
the new cooling holes 110 may extend between the outer and inner surfaces
108 and 104, respectively, as shown. The new cooling holes 110 may be
installed through the old cooling holes 66, 68, or 70, may be drilled
through part of the old cooling holes 66, 68, or 70, or may be drilled
through portions outside the old cooling holes 66, 68, and 70, as shown
in FIG. 7. Furthermore, the old cooling holes 66, 68, and 70, now
obstructed with filling agent 100, may retain enough structure after the
installation of new cooling holes 110 such that cooling fluid only passes
through the new cooling holes 110. Although FIG. 7 shows cooling holes
110 extending substantially perpendicularly through substrate wall 60
with respect to outer and inner surfaces 108 and 104, the new cooling
holes 110 may be obliquely oriented with respect to surfaces 108 and 104
or may adopt other orientations as well. The shapes, sizes and
orientations of the new cooling holes 110 may be determined by the
skilled artisan according to each application.

INDUSTRIAL APPLICABILITY

[0063] From the foregoing, it can be seen that the present disclosure
describes the closure of cooling holes in a substrate wall with enamel or
ceramic paste after the removal of an original TBC layer (or otherwise
exposing an outer surface of the substrate wall), the application of a
new TBC layer on the outer surface of the substrate wall, the
installation of new cooling holes, and the gas turbine engines using the
resulting modified substrate wall. Such method of blocking the cooling
holes and processes to improve or repair gas turbine engines may find
industrial applicability in many applications including, but not limited
to, aerospace applications such as airplanes.

[0064] Current trends in gas turbine engine design are requiring a
flexible approach to modify or fill cooling holes in substrate walls. By
taking advantage of the sealant ability of enamel or ceramic paste, their
stability at elevated temperatures, their ability to obstruct air flow
passage through the cooling holes when cured, and their ability to
provide engine component walls with structural compactness such that
newly applied TBC layers are associated with spallation resistance, the
present disclosure provides a novel solution to afford an efficient
strategy to fill cooling holes in gas turbine engine components with low
cost and high flexibility. Since the modification may generate a modified
substrate wall having a new TBC with a new pattern for cooling holes, the
present disclosure is advantageous when compared to manufacturing a new
substrate wall from scratch. Furthermore, since the filling agent
materials left in the new structure wall have good thermal and structural
stability during operation, it may become part of the new structure
without interfering with the engine operation. Moreover, using the novel
strategy to repair and modify the structure wall according to the present
disclosure opens up new possibilities for gas turbine engines which may
reduce costs associated with time-consuming, inflexible, and expensive
manufacturing processes.

[0065] While the invention has been described with reference to certain
embodiments, it will be understood by those skilled in the art that
various changes may be made and equivalents may be substituted for
elements thereof without departing from the scope of the invention. In
addition, many modifications may be made to adapt to a particular
situation or material to the teachings of the invention without departing
from the essential scope thereof. Therefore, it is intended that the
invention not be limited to the particular embodiments disclosed as the
best mode contemplated for carrying out this invention, but that the
invention will include all embodiments falling within the scope of the
appended claims.